REM sleep and its mechanism-an updated review

Normal human sleep comprises of two states rapid eye movement (REM) and Non-REM (NREM), which alternates cyclically across a sleep episode. REM sleep was identified by its most typical behavior rapid eye movements during sleep. Electroencephalogram (EEG) of neocortex of most mammals exhibit desynchronized,low-amplitude, and high frequency fast character previously seen in waking, but behavioral sleep persists. This state of sleep called as paradoxical sleep or activated sleep or activated brain in a paralyzed state. Hippocampus has regular high voltage theta waves throughout REM sleep. Multiple neuro-scientific and physiological studies were done to understand the mechanism and genesis of REM sleep. Results of different studies analyze that REM sleep is executed by widely distributed network, rather than single REM sleep center. A number of studies have been attempted to identify pedunculopontine tegmentum (PPT) cholinergic cells present in brainstem, which when activated causes generation and modulation of REM sleep when compared with either NREM or waking. REM sleep sign generator remains in Turned-off condition when aminergic and cholinergic neurotransmitter ratio is1:1 and generator is turned-on to express REM sleep signs when the ratio is 0:0.65. REM-on cells use the neurotransmitter GABA, Ach, glutamate, and glycine, whereas REM-off cells use nor-epinephrine,serotonin, and histamine. c-AMP-PKA intracellular signaling pathway is critically involved in cholinergic cell compartment of the PPT for regulation of cholinergic tone in REM sleep-sign-generators. This review reflects the recent updates on cellular and molecular mechanisms in regulation of REM sleep.